One of my jobs as a liquid fuels maintenance tech in the Air Force was to clean above ground and below ground bulk storage fuel tanks. Some of the above ground tanks were massive, 1/2 million gallons. Back then the AF used JP-4. It was volatile sh*t. The above ground tanks had lids that floated on the fuel to cut down on evaporation. You just couldn't have that much fuel exposed to the elements. This lid had 6' legs that supported it when the tank was empty. Our job was to empty the tank(s) then vent all of the vapor out from under the lid. One time when I was at Castle AFB we were cleaning a tank. We had sucked most of the vapor out of the tank but the lid's rubber seal was damaged and was leaking some fuel (the seal that went all the way around the diameter of the lid was stuffed with foam rubber) that had gotten into the seal. Because of that, the environment was pretty hairy.
We had to climb up the side of the tank and then descend down a ladder onto the top of the lid. It's weird because you are inside a giant can of gas. The tank is probably 40 feet tall. The lid is sitting on 6' legs, and you know underneath you is a lot of fuel vapor. You just hope you sucked enough of the vapor out so if there's a problem it won't go off like a cannon.
When we were examining the lid seal the damn thing tore away from the weight of the fuel inside of it. As it slid down the inside of the tank it caught fire! Luckily the fire was away from the ladder so we ran like hell up that ladder, then back down the other side to safety. Thankfully we had sucked all the vapor out, otherwise it would have gone boom! It's hard to explain, but it was probably the scariest experience I have ever had. I kept thinking inside my head as I ran, "don't blow, don't blow!"
It didn't blow because we had done our job by sucking enough fuel vapor out that even with the additional fuel from the broken seal, there was not enough for an explosion.
Our maintenance chief had been in an explosion at the same location 10 years earlier. A contractor was doing the job. They cut some corners and the resulting blast killed 2 people.
Then there were the underground tanks. Oh boy, I did not like those things. Scared me silly.
p.s. When I was at Osan, they were building a truly massive tank. It was half underground, half above ground with a dome on it. I left in 1984 before the tank was completed. In 1985 when they were filling it up for the very first time static electricity built up inside of it setting off a massive explosion that killed something like 18 people who were in the vacinity. That's how crazy that dang JP-4 was. Any kind of movement, be it fuel rushing into the tank, people walking, could release a static charge that could set it off. I hated it!